linux-kernel - [PATCH 2/2] regmap: debugfs: improve regmap_reg_ranges_read

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Message-Id: <1443479342-31621-2-git-send-email-linux@rasmusvillemoes.dk>
Date:	Tue, 29 Sep 2015 00:29:02 +0200
From:	Rasmus Villemoes <linux@...musvillemoes.dk>
To:	Mark Brown <broonie@...nel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	Rasmus Villemoes <linux@...musvillemoes.dk>,
	linux-kernel@...r.kernel.org
Subject: [PATCH 2/2] regmap: debugfs: improve regmap_reg_ranges_read_file()

* A page is a bit much for two integers and a bit of punctuation. 64
  bytes should suffice.

* Calling strlen() on entry no less than three times is silly,
  especially when snprintf() has returned that value (which was just
  thrown away).

* Transferring entry to the output buffer using snprintf is silly,
  when we know the length. Use memcpy instead.

* Making the newline part of entry, we can avoid having to account for
  it separately in multiple places.

Signed-off-by: Rasmus Villemoes <linux@...musvillemoes.dk>
---
 drivers/base/regmap/regmap-debugfs.c | 19 +++++++++----------
 1 file changed, 9 insertions(+), 10 deletions(-)

diff --git a/drivers/base/regmap/regmap-debugfs.c b/drivers/base/regmap/regmap-debugfs.c
index 9fb3f6fc26b0..01110c0b8be0 100644
--- a/drivers/base/regmap/regmap-debugfs.c
+++ b/drivers/base/regmap/regmap-debugfs.c
@@ -333,6 +333,8 @@ static ssize_t regmap_reg_ranges_read_file(struct file *file,
 	char *buf;
 	char *entry;
 	int ret;
+	unsigned entry_len;
+	const unsigned entry_size = 64;
 
 	if (*ppos < 0 || !count)
 		return -EINVAL;
@@ -341,7 +343,7 @@ static ssize_t regmap_reg_ranges_read_file(struct file *file,
 	if (!buf)
 		return -ENOMEM;
 
-	entry = kmalloc(PAGE_SIZE, GFP_KERNEL);
+	entry = kmalloc(entry_size, GFP_KERNEL);
 	if (!entry) {
 		kfree(buf);
 		return -ENOMEM;
@@ -360,18 +362,15 @@ static ssize_t regmap_reg_ranges_read_file(struct file *file,
 	p = 0;
 	mutex_lock(&map->cache_lock);
 	list_for_each_entry(c, &map->debugfs_off_cache, list) {
-		snprintf(entry, PAGE_SIZE, "%x-%x",
-			 c->base_reg, c->max_reg);
+		entry_len = snprintf(entry, entry_size, "%x-%x\n",
+				     c->base_reg, c->max_reg);
 		if (p >= *ppos) {
-			if (buf_pos + 1 + strlen(entry) > count)
+			if (buf_pos + entry_len > count)
 				break;
-			snprintf(buf + buf_pos, count - buf_pos,
-				 "%s", entry);
-			buf_pos += strlen(entry);
-			buf[buf_pos] = '\n';
-			buf_pos++;
+			memcpy(buf + buf_pos, entry, entry_len);
+			buf_pos += entry_len;
 		}
-		p += strlen(entry) + 1;
+		p += entry_len;
 	}
 	mutex_unlock(&map->cache_lock);
 
-- 
2.1.3

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